Current active organic light emitting diode (OLED) devices are typically controlled by thin film transistors (TFTs). Therefore, if an OLED device of the bottom emission structure emits light in the form of a bottom exit, the light emitted from the bottom is blocked by the TFTs and the metal wire circuits formed on the substrate when passing through the substrate, so that the area of the actual light emission is limited, resulting in a reduced ratio of light emitting area, which is the so-called aperture rate. In addition, in order to improve the brightness difference between pixels, many of the currently studied OLEDs employ pixel structures with compensation circuit in which pixel circuits such as 2T1C or higher are used. In this case, the aperture ratio of the OLED device of the bottom emission structure is further reduced. The top emitting OLED device has a great advantage over the bottom emitting OLED device, which increases the aperture ratio and extends the life of the device. For large-sized top emitting OLED devices, the cathode structure is critical.
Generally, the cathode of an OLED device may be prepared in two ways. In the first method with simpler process, a metal such as a magnesium-silver alloy is generally used as a cathode. However, due to the need for transparency, the metal needs to be formed to be very thin, which will result in a larger resistance, serious resistive voltage drop (IR drop), and poor uniformity of the OLED panel, which in turn affects the application of this process in large sized panels. In the second method, a transparent metal oxide such as indium zinc oxide (IZO) is used as the cathode. As the transparent metal oxide film material has a relatively high transparency, the resistance can meet the performance requirements of the device even when the thickness is large. However, since the transparent metal oxide material needs to be prepared by a sputtering process, the energy used at the time of sputtering is large, and the OLED device is liable to be damaged, thereby affecting the performances such as implantation efficiency and lifetime of the OLED device.
It should be noted that, information disclosed in the above background portion is provided only for better understanding of the background of the present disclosure, and thus it may contain information that does not form the prior art known by those ordinary skilled in the art.